Stepping motor structure

ABSTRACT

A dynamoelectric machine having a stator enclosed in a rotor, the stator including spider-like projections each having teeth which coact with teeth on the interior of the rotor. The operating windings are located on the legs of the stator spider. A cylindrical permanent magnet provides an operating magnetic bias, and a flux guiding element steers the flux appropriately. A single-ended and a balanced embodiment are disclosed.

United States Patent 11 1 Abraham et a1.

[ 1 Sept. 18, 1973 STEPPING MOTOR STRUCTURE Inventors: Dennis G. Abraham, Vestal; George J. Dohanich, Endicott; Frederick W. Doolittle, Binghamton; Stephen H. Mills, Newark Valley, all of NY.

Assignee: International Business Machines Corporation, Armonk, N.Y.

Filed: May 15, 1972 Appl. No.: 253,064

US. Cl 310/49, 310/67, 310/154 Int. Cl. "02k 37/00 Field of Search 310/49, 67, 112,

References Cited UNITED STATES PATENTS 2/1970 Barrett 310/67 754,802 3/1904 Porsche 310/67 3,179,825 4/1965 Terry 3,500,081 3/1970 Drejza 3,561,834 2/1971 Durand 765,078 7/1904 Jigouzo 2,952,788 9/1960 Volkerling 310/154 Primary ExaminerR. Skudy Attorney-Paul M. Brannen et al.

A dynamoelectric machine having a stator enclosed in a rotor, the stator including spider-like projections each having teeth which coact with teeth on the interior of the rotor. The operating windings are located on the legs of the stator spider. A cylindrical permanent magnet provides an operating magnetic bias, and a flux guiding element steers the flux appropriately. A singleended and a balanced embodiment are disclosed.

ABSTRACT 7 Claims, 4 Drawing Figures STEPIING MOTOR STRUCTURE BACKGROUND OF THE INVENTION Dynamo-electric machines of the inside-out type, in which the inner portion is the stator element, and an outer shell acts as a rotor, are known in the art, as for example U. S. Pat. No. 3,179,825. This invention provides a greatly simplified construction of such a machine, particularly suited for stepper motor operation, utilizing only a small number of parts.

SUMMARY OF THE INVENTION Briefly described, the present invention comprises a cylindrical rotor mounted for rotation on a shaft which supports a stator structure, having a plurality of radially aligned teeth which cooperate with other teeth on the interior of the rotor. The stator comprises a plurality of outwardly extending portions or spokes, each provided with an appropriate coil or winding. The windings, sequentially energized, provide the operating flux for the motor. A circular permanent magnet, mounted on the shaft, provides a biasing flux. A flux focusing or guiding member is also mounted on the shaft to steer the flux in the optimum paths. A plurality of conventional tractor pins may be provided around the outer periphery of the rotor, to engage feed holes in a paper web, whereby the motor affords an improved continuous-web document feeding means.

Accordingly, it is a principal object of this invention to provide an improved stepping motor structure, in which the rotor surrounds and rotates about the stator.

Another object of the invention is to provide an improved stepping motor of the type described, in which a circular permanent magnet is provided for biasing purposes and is located within the rotor.

Still another object of the invention is to provide an improved motor of the type described, in which a circular flux focusing member is mounted on the shaft within the rotor, to steer the flux in the motor.

The foregoing and other objects, features and advantages of the invention will be apparent from the followcup-shaped outer shell or rotor is mounted on shaft ing more particular description of preferred einbodiments of the invention, as illustrated in the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a longitudinal sectional view of amotor constructed in accordance with a first embodiment of the invention;

FIG. 2 is a sectional view taken along the axis of rotation of FIG. 1;

FIG. 3 is a longitudinal sectional view of a motor con structed in accordance with a second embodiment of the invention; and

FIG. 4 is a sectional view taken along the axis of rotation of FIG. 3.

Similar reference characters refer to similar parts in each of the several views.

Referring to the first embodiment of the invention, illustrated in FIGS. 1 and 2, FIG. 1 shows a crosssectional view of the stepping motor according to the first embodiment of the invention, taken along the axis of the motor. As shown in the drawings, the stationary shaft 3 has mounted thereon a stator spider or core as- 6 sembly having a plurality of radially extending portlons or spokes 5, each of which is enlarged at the outer end thereof and provided with the plurality of teeth or pole 3 by means of a suitable bearing 17 and carries around its periphery a plurality of pins 19 which may be utilized for engaging holes in the edge of a paper web when the motor is used as a document transport device. The inner surface of the rotor 15 is grooved or fluted so as to produce a plurality ofinwardly extending teeth, a few of which are designated by reference character 21. The faces of these teeth have the same dimensions as those on the stator. In one particular arrangement of the type shown in FIGS. I and 2, each of eight spokes or poles 5 has four teeth at the outer end thereof, with bifilar coils wound on the pole pieces. The stator is provided with 48 teeth spaced at 7.5 intervals. The diameter is selected so that the periphery advances 1/6 inch for each 7.5 increment. Operating as a normal stepping motor, it has a step angle of 1.875", thus requiring four steps to advance 7.5. This simplifies the logic design and system synchronization. The pole pieces are each advanced A of a tooth pitch to provide operation as set forth in U. S. Pat. No. 2,589,999.

Referring now to the second embodiment of the invention, as shown in FIGS. 3 and 4, it is principally distinguished by a balanced construction. Two sets of identical stator elements 5 are provided, one at each end of the rotor cylinder 15. The rotor is supported for rotation by the non-magnetic end caps 23, on the bearings 17. The permanent magnet is in the form of a cylinder 11, with the flux focusing member 13 extending between the shaft 3 and the radially oriented magnet 11. In this case, the stator elements 5 are skewed A tooth pitch with respect to each other.

By separating the stator into two elements, a larger window area is provided for the windings allowing more tooth area, heavier saturation or cooler operating temperatures, or some combination of these advantages. The magnetic flux path is divided and shortened, thus reducing losses due to eddy currents, etc. The permanent magnet is located close to the teeth of the motor, improving the coupling and reducing the size of the magnet.

From the foregoing, it will be apparent that a step-' ping motor constructed in accordance with the present invention provides an efficient economical stepping motor, whose inside-out construction makes it adaptable to functions such as continuous form feeding.

While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that the foregoing and other changes in form and details may be made therein without departing from the spirit and scope of the invention.

We claim:

1. A stepping motor comprising:

a stator, fixedly mounted on a shaft, said stator comprising a spider having a plurality of spokes radially extending outward from the shaft,

operating windings disposed on said spokes and effective when energized to generate magnetic flux in said spokes, the direction of flux being radial,

an enlarged pole piece section at the outer end of each of said spokes, said sections each being provided with a plurality of radial teeth,

a rotor surrounding and substantially enveloping said stator, said rotor comprising a cylinder having a plurality of teeth on the inner surface thereof corresponding in dimension to the teeth of said stator, the teeth on said stator and the teeth on said rotor being skewed or advanced with respect to one another by one quarter of a pole pitch, said rotor being mounted for rotation on said shaft,

a permanent magnet flux source for providing an operating flux bias for said motor, said magnet comprising a circular magnet member concentric with said shaft and said rotor, and

flux focusing means associated with said magnet for directing the flux from said magnet in a preferred path including said rotor and said stator.

2. A stepping motor as claimed in claim 1, in which said permanent magnet comprises a ring-shaped magnet concentric with said shaft, and located at the closed end of said rotor, and said flux focusing means comprises a tapered cylindrical member extending axially from said magnet to said spider.

3. A stepping motor comprising a stator fixedly mounted on a shaft, said stator having a first and a second spider, each comprising a plurality of spokes radially extending outward from the shaft, said spiders being disposed at opposite ends of the motor,

operating windings disposed on said spokes and effective when energized to generate magnetic flux in said spokes, the direction of flux being radial,

an enlarged pole piece section at the outer end of each of said spokes, said sections each being provided with a plurality of radial teeth,

a rotor surrounding and substantially enveloping said stator, said rotor comprising a cylinder having a plurality of teeth on the inner surface thereof corresponding in dimension to the teeth of said stator, said rotor being mounted on bearings at opposite ends of said motor for rotation on said shaft,

a permanent magnet flux source for providing an operating flux bias for said motor, said magnetcomprising a circular magnet member concentric with said shaft and said rotor, and

flux focusing means associated with said magnet for directing the flux from said magnet in a preferred path including said rotor and said stator, said flux focusing means comprising a circular magnetic element fitting between said magnet and said shaft,

said permanent magnet and said focusing means being disposed centrally on said shaft with respect to said first and second spiders.

4. A stepping motor as claimed in claim 3, in which said permanent magnet is radially magnetized.

5. A stepping motor as claimed in claim 3, in which the teeth on said stator teeth and said rotor teeth are skewed or advanced with respect to one another by an even fraction of a pole pitch.

6. A stepping motor as claimed in claim 5, in which the fraction is one-quarter of a pole pitch.

7. A stepping motor as claimed in claim 3, in which the outer surface of said rotor is provided with load engaging means.

* III I l 

1. A stepping motor comprising: a stator fixedly mounted on a shaft, said stator comprising a spider having a plurality of spokes radially extending outward from the shaft, operating windings disposed on said spokes and effective when energized to generate magnetic flux in said spokes, the direction of flux being radial, an enlarged pole piece section at the outer end of each of said spokes, said sections each being provided with a plurality of radial teeth, a rotor surrounding and substantially enveloping said stator, said rotor comprising a cylinder having a plurality of teeth on the inner surface thereof corresponding in dimension to the teeth of said stator, the teeth on said stator and the teeth on said rotor being skewed or advanced with respect to one another by one quarter of a pole pitch, said rotor being mounted for rotation on said shaft, a permanent magnet flux source for providing an operating flux bias for said motor, said magnet comprising a circular magnet member concentric with said shaft and said rotor, and flux focusing means associated with said magnet for directing the flux from said magnet in a preferred path including said rotor and said stator.
 2. A stepping motor as claimed in claim 1, in which said permanent magnet comprises a ring-shaped magnet concentric with said shaft, and located at the closed end of said rotor, and said flux focusing means comprises a tapered cylindrical member extending axially from said magnet to said spider.
 3. A stepping motor comprising a stator fixedly mounted on a shaft, said stator having a first and a second spider, each comprising a plurality of spokes radially extending outward from the shaft, said spiders being disposed at opposite ends of the motor, operating windings disposed on said spokes and effective when energized to generate magnetic flux in said spokes, the direction of flux being radial, an enlarged pole piece section at the outer end of each of said spokes, said sections each being provided with a plurality of radial teeth, a rotor surrounding and substantially enveloping said stator, said rotor comprising a cylinder having a plurality of teeth on the inner surface thereof corresponding in dimension to the teeth of said stator, said rotor being mounted on bearings at opposite ends of said motor for rotation on said shaft, a permanent magnet flux source for providing an operating flux bias for said motor, said magnet comprising a circular magnet member concentric with said shaft and said rotor, and flux focusing means associated with said magnet for directing the flux from said magnet in a preferred path including said rotor and said stator, said flux focusing means comprising a circular magnetic element fitting between said magnet and said shaft, said permanent magnet and said focusing means being disposed centrally on said shaft with respect to said first and second spiders.
 4. A stepping motor as claimed in claim 3, in which said permanent magnet is radially magnetized.
 5. A stepping motor as claimed in claim 3, in which the teeth on said stator teeth and said rotor teeth are skewed or advanced with respect to one another by an even fraction of a pole pitch.
 6. A stepping motor as claimed in claim 5, in which the fraction is one-quarter of a pole pitch.
 7. A stepping motor as claimed in claim 3, in which the outer surface of said rotor is provided with load engaging means. 